Problem importing the blender model into unity
In Blender you need to rename the bone AND any weight groups you have already assigned when parenting to the armature. The armature bone name needs to match the weight group created for the mesh, otherwise the foot won't be moving with the bone in Blender or in Unity.

Additionally in Unity you can go to Rig-tab and click the button configure the avatar where you can manually assign the left foot to the bone that your model has. But I assume if you fix the weight group naming first (which is mandatory for the rig to work) Unity should be able to correctly automatically detect the foot afterwards.

Finally after you have configured the avatar you can proceed to importing the animations.